A project of the next generation mobile radio network in a third generation partnership project (3GPP) is a system architecture evolution (SAE). FIG. 1 shows a schematic diagram of an SAE architecture. As shown in FIG. 1, the SAE architecture includes but not limits to the following network elements:
Evolved radio access network (E-RAN) provides a higher uplink and downlink rate, lower transmission delay and more reliable radio transmission. A network element included in the E-RAN is an evolved NodeB (eNodeB), which provides radio resource of an access of a terminal.
A home subscriber server (HSS) is arranged to permanently store a subscriber data.
A mobility management entity (MME) is a control plane functional entity and is also a service for temporarily storing user data. The MME is arranged to manage and store context of an user equipment (UE) (for example: UE/user identifier, mobility management state and user security parameter etc.), allocate a temporary identifier for users. Furthermore, when the UE is in a tracking area or a network is in charge of authenticating the users, the MME processes all the non-access layer messages between the MME and the UE, and trigger a paging in the SAE.
A serving gateway is a user plane entity, which is in charge of a user plane data routing process, ending downlink data of the UE in an idle state, managing and storing a context of the SAE bearer of the UE, for example: interne protocol (IP) bearer service parameters and network internal routing information and so on. The serving gateway is further an anchor of an user plane in the 3GPP system, and each user is configured with only one serving gateway at one moment.
A grouped data network gateway (PDN GW) is a gateway that in charge of accessing of the UE to the PDN, allocating user IP address, and is further a mobile anchor in a 3GPP and non 3GPP access system. And users can access to multiple PDN GW at the same time.
A policy and charging rule functionality (PCRF), which generates, according to service information, subscriber information and configuration information of an operator, quality of service rules and charging rules used for controlling user data transmission. And the functionality further controls establishing and releasing of a bearer in the access network.
Service of voice, video etc. based on an IP can be provided by allocating an IP multimedia subsystem (IMS) network in the next generation mobile network, to replace a circuit switched (CS) domain in a 2G/3G network. The voice service of the terminal can be transmitted through an LTE bearer. Currently, mainstream operator allocates a special access point name (APN) for long-term evolution bearer voice (VoLTE), the network and the terminal establish a default bearer that a QoS class identifier (QCI) is 5 for the APN, which is used for transmitting a signaling needed by a user when registered in the IMS network, called a signaling bearer. When the terminal calls or be called, a special bearer that the QCI is 1 is established temporarily for the terminal, which is used for transmitting a voice data, called a voice bearer. When the calling is finished, the voice bearer is released.
When the user calls or be called, a voice bearer is established for the terminal by the network, thus, a call establishing time delay is very long. If the terminal is on the cell edge and in a switching process, a VoLTE calling occurs, then a conflict between the switching process and the voice bearer establishing process on the network side will occur. According to a standard realizing manner in current 3GPP, the switching process is finished by a base station at first, the NAS message is discarded during the switching process, and the voice bearer establishing process may be given up or delayed by a core network, then the user call will not succeed or the call establishing time delay is prolonged, and user experience is affected.